Breast cancers that are resistant to therapy frequently recur years after treatment of the initial disease. Eradication of these recalcitrant cancers depends upon understanding the origins of death-resistance (DR), and the mechanisms underlying tumor dormancy. We have shown a) signaling through the basement membrane (BM) integrins a3/b1 and a6/b4 induces S-1 nonmalignant human HMT-3522 mammary epithelial cells (S-1 MECs) to growth-arrest and form polarized acini, whereas their malignant counterparts (T4-2) fail to growth-arrest or form polar acini in response to these same signals, b) S-1 MECs are dependent on a3/b1-integrin signaling for survival, whereas following malignant transformation (T4-2) they become independent of b1-integrin signaling, c) instead of dying, inhibition of either b1-integrin or epidermal growth factor receptor (EGFR) activity in these T4-2 MECs, induces them to growth-arrest, form polarized acini ('phenotypic reversion', T4-R), and survive in a 'dormant' state, and d) this 'phenotypic reversion' occurs only in the presence of a malleable BM, where these T4-2 MECs receive both the correct biochemical and spatial signals, which allow them to cross-modulate their adhesion and growth factor receptors. We recently found e) that the polarized acini of both S-1 and T4-R MECs are DR to a number of disparate 'apoptosis-inducing' stimuli. As such we have derived the following hypothesis: that given the correct biochemical and spatial cues from the extracellular matrix (ECM), subgroups of tumor cells survive to become dormant and recalcitrant to therapy by exploiting specific integrin-linked pathways. Upon examination we found the BM-induced DR in S-1 and T4-R MEC acini is associated with ligation of a6/b4-integrins and tissue polarity. Thus the objective of these studies is to understand how the BM induces DR in polarized MEC acini via a6/b4-integrins. We will use the HMT-3522 S-1 nonmalignant and T4-2 tumor MEC model, 3D ECM assays and cell and molecular approaches to: 1. Determine how BM signaling through a6/b4-integrins, tissue polarity, acini organization and DR are related. Approaches include testing whether a6/b4-integrins can direct DR in the absence of polarity and a 3D acinar structure, and if not, what degree of polarity or structural organization is necessary. 2. Delineate the minimal signaling events linked to a6/b4-integrin-induced DR by: manipulating a6/b4-integrin-directed hemidesmosome assembly and intracellular signaling through PI3kinase and Shc. 3. Initiate studies to elucidate how DR is induced in MECs through a6/b4-integrins by: examining the relationship between p53 status and a6/b4-integrin induced DR and determining where the apoptotic pathway is blocked. These studies should lead to rational approaches to develop alternate therapies.